HMC701LP6CE datasheet(17/40 Pages) AD

17 / 40 page

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HMC701LP6CE

v09.1112

8 GHz 16-BIT FRACTIONAL-N PLL

flag ro_lock_detect (Reg1Fh<0> table 41) will be set. a single occurrence outside of the window will result in clearing

the Lock Detect flag, ro_lock_detect.

the Lock Detect flag ro_lock_detect (Reg1Fh<0> table 41) is a read only register, readable from the serial port. the

Lock Detect flag is also output to the LD_SDO pin according to lkd_to_sdo_always (Reg1Ah<13>) and lkd_to_sdo_

automux_en (Reg1Ah<12>), both in table 36. Setting lkd_to_sdo_always will always display the Lock Detect flag

on LD_DSO. clearing lkd_to_sdo_always and setting lkd_to_sdo_automux_en will display the Lock Detect flag on

LD_SDO except when a serial port read is requested, in which case the pin reverts temporarily to the Serial Data out

pin, and returns to the lock detect function after the read is completed.

Figure 11. Normal Lock Detect Window

Lock Detect with Phase Offset

When operating in fractional mode the linearity of the charge pump and phase detector are more critical than in

integer mode. the phase detector linearity is worse when operated with zero phase offset. Hence in fractional mode

it is necessary to offset the phase of the reference and the Vco at the phase detector. in such a case, for example

with an offset delay, as shown in Figure 12, the mean phase of the Vco will always occur after the reference. the

lock detect circuit window can be made more selective with a fixed offset delay by setting win_asym_enable and

win_asym_up_select (Reg1Ah<11> table 36). Similarly the offset can be in advance of the reference by clearing

win_asym_up_select while leaving win_asym_enable Reg1Ah<10> set both in table 36.

Figure 12. Delayed Lock Detect Window

For most applications the analog one shot window is sufficient. to determine the required Lock Detect one shot

window size:

required LD one Shot Window = (cP Phase offset (ns) + 4xtvco) x 1.3

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